Production of anhydrous alkali metal hyposulphites



Patented Aug. 6, 1935 PATENT OFFICE ,PRODUCTION OF ANHYDROUS ALKALI METAL HYPQSULPHITES Byron M. Vanderbilt and Howard Adler, Chicago Heights, 1118,

, assignors to ;Victor.

Works, a, corporation of Illinois 3 No Drawing. Application Chemical July 1, 1933,

, Serial No. 683,096 3 :15 Claims. (01. 23-116). q

This invention relates to the production of 'anhydrous alkalfmetal hyposulphit es; It has heretofore been proposed to carry out the production ofanhydrous alkalimetal hy'posul- 5 phites in strong ethyl alcohol, by the interaction of sodium or other alkali metal sulphite, compounds and alkali Ior nates; "Such a method, howeVenanord's a product of-relatively low stability and purity, and requires an alcohol "containing relatively little water.

By means'of the present invention anhydrous alkali metal hyposulphitesof highpuri'ty and stability are produced, and at 'thesame time the method is more readily carried out because a larger proportion'of water is permissible. The use of the more dilute solvent greatly facilitates the formation of 'the hyposulphite. "Likewise, it

is possible touse'more impure formate than pre viously, while still obtain'inga'l better" purity in the In accordance with the present invention, it is preferred to'use as startingmaterials an alkali metal compound of theclass consisting of hydroxides andcarbonates an alkali metal formate and sulphur'dioxide. 1 It has been discoyered that with these starting materialsthe' diiilculties due to'the presence of impurities in alkali metal bisulphites and pyrosulphites arelovercomefsince there is no opportunity for the oxidationfof any 0 sulphites formed intermediately. "The use of analkali metal carbonate is pre ferred over the use of caustic alkali because the reaction of the sulphur dioxide liberates carbon dioxide, which acts to sweep out of themixture any oxidizing gases which may be presentthereby preventing-partial oxidation of the hyposulphitef l p .It isiikewise preferredfinsteadbf using an ethyl alcohol solutioniniaccordance with the prior 4 art, to'use a solution-containingmethyl'alcohol,

either in combination with ethyl alcohol or alone. For example, in using ethyl alcohol 'alone'git was found that 'the' presence of more than 21% :by weight of water caused" coagulation and partial decomposition, of the hyposulphite as it was forni'ed 'and resulted in an unstable sticky solid mass; By replacing part or all of the ethyl alcohol by methanol it'is possible to use a considerably more 'dilute solution without thisdecomposition,

and at the same time produce alcornpound o f higher purity and greater stability with solutions above the critical point.

Ithas likewise been discovered that by adding sulphur dioxide to the mixture at a temperature below 30? C. the final product is of larger particle size and more stable than when the sulphur di oxide is-added at higher temperatures. Further, the addition of thesulphur dioxide at any temperature below that necessary for the formation of the 'hypos ulphita permits the introduction of the full amount of this reagent required before any reaction to form hyposulphite takes place. In-this way, it is-possible to use sulphur dioxide directly from the combustion of sulphur, without the necessity of removing excess oxygen from-the combustion gases, since noappreciable amount of this oxygen is retained in the solution. This permits the useof an exceedingly cheap method of making the sulphur dioxide for the process.

, It is also advisable to introduce the sulphur dioxideinto an alcohol solution of the reagents rather than into an aqueous solution to which the alcohol issubsequently added. he hyposulphite is only one of a large number of compounds which may be formed from these ingredients. In order to obtain high yields and a pure product, it is therefore necessary to control carefully the reactionconditions. It is preferred, after introducing all of the'sulphur dioxide, to heat the mixture rapidly to a temperature be tween 50 and C., at whichpoint the hyposulphite formation begins. Thereafter the temperature isgradu'allyraisecl for about one hour to -76 0.; and is maintained at this point for about 4 to 5 hours. Overheating should be avoided, since this will cause decomposition of the hyposulphite. Decomposition is indicated by coagulatiori'of the precipitate; e l It wasfurther discovered that the purity an the stability of the hyposulphite product can be increased by washing the precipitate with methanolrather than anhydrous ethyl alcohol. This isbelieved to be due to the fact that most of the impurities, such as sodium thiosulphate, sodium formate, etc.', are more soluble in methanol than in ethyl alcohol. The methanol is also more easily'dried out'of the product and can be more readilyrecovered for re-use. i

The drying of the product should be carefully controlled; It is preferredto dry at room temperatures under a high vacuum (less than20 mm. of mercury) until the product becomes dusty, after which the temperature is increased toa point below 125 0., andpreferably around C. until the product is completely dry and free of methanol. By following this procedure/the product will be free'from obnoxious organic odors and will show a minimum tendency to cake in storage. T

F'I'he reaction 7 2,0 1 0,6 1 5 below 125 C. until the methanol is completely removed. Y

12. The method of preparing an anhydrous alkali metal hyposulphite which comprises reacting an'alkali metal formate, sulphur dioxide, and an alkali metal compound of the class consisting of hydroxides and carbonates, in an aqueous solution of methyl alcohol, said reaction being carried perature below 30 0., and the reaction mixture is then heated quickly to 50-55 C. and then is slowly heated to 65-76 C., and is maintained at this temperature until the hyposulphite formation is substantially complete.

15. The method of preparing an anhydrous alkali metal hyposulphite which comprises reacting an alkali metal formate, sulphur dioxide and an alkali metal compound capable of forming a pyrosulphite or bisulphite with sulphur dioxide, in asolution of methyl and ethyl alcohol containing a substantial quantity of water.

BYRON M. VANDERBILT.

HOWARD ADLER. 

